it's likely due to the complications involved with his omega identity. He's kept it secrect for so long that the idea of confessing now would likely put him in a dangerous position considering his moms past actions and the way the empire would view him. If the civilians of the empire view Etienne as a liar then they won't want him to share the throne as a leader. There's also fear from the current emperor that Etienne would still be on his moms side causing him to reject the idea of a marriage.
It’s banned for omegas to rule so either way I don’t think they’ll allow it since he’s been lying the whole time and he is first in line for the throne but he’s an omega so yea they’re not gonna let him be either way
I just remember that omegas were banned not because of the typical "omegas weak and exist only to produce offspring" kinda stereotype, but because omegas with potent pheromone can literally influence others and can be a very deadly tyrant.
Idk if i’m misunderstanding something but why can’t they just reveal his omega identity after exposing the empress / stripping her of power, then have a political marriage to unite both sides since they like each other anyways.